Visualisations - add tree panel to analysis output displays

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The system currently only displays the selected tree in the View Labels tab.  

It would be useful to also display the tree in the analysis outputs.  That way 
one could, for example, interrogate the tree while also visualising the PD or 
PE results from a spatial analysis.  

The system should allow the user to choose between the currently selected tree, 
the tree used in the analysis, and possibly also any trees generated by the 
indices (e.g. the PE analyses use a trimmed tree).  The latter option will need 
indices objects to be retained as currently they are destroyed.  

Ideally the system should also be able to link indices back onto the tree.  For 
example, some list indices give values for each node in the tree.  The nodes 
could be coloured based on these values.  

Original issue reported on code.google.com by shawnlaffan on 30 Oct 2013 at 11:12

• Blocking: GUI - Improve pan, zoom, etc. controls #353
• Blocked on: GUI - allow user to control the width of the branches #505